"non-cleric," early 15c., from lay (adj.) + man (n.). Similar formation in Old Frisian lekman, Danish lægmand. Meaning "outsider, unprofessional person, non-expert" (especially in regards to law or medicine) is from late 15c. Related: Laymen.
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Definitions of layperson from WordNet
someone who is not a clergyman or a professional person;